Northern transfer analysis of viral-specific RNA from one of transformed clones of Moloney murine sarcoma virus infected mouse 3T3 FL S plus L- cells and revertant subclones demonstrated the presence of several RNA size classes, 30S, 25 to 23S and 21S. The 30 S RNA was lost from cellular RNAs of the rescue-negative revertants. The largest viral-specific RNA present in Moloney murine leukemia virus producing mouse cells was 35S.